Monday afternoon, Duke coach Mike Krzyzewski discussed the improbability of an undefeated college basketball season. Tuesday evening, even as his top-ranked Blue Devils remained unscathed, his words rang true.

The first component Krzyzewski mentioned was “health.” A key injury can derail the best of teams, as Duke learned two seasons ago, when a toe ailment sidelined freshman Kyrie Irving from early December until March.

That squad opened the season 15-0, and with Irving, Krzyzewski thought it capable of becoming the sport’s first unbeaten champion since Indiana in 1976. Without Irving, the Blue Devils finished second in the ACC during the regular season and won the league tournament.

Irving returned for the NCAAs, but Duke lost to Arizona in a regional semifinal and finished 32-5.

Well, Duke has again opened 15-0 and Saturday faces what figures to be among its most challenging conference games: at preseason favorite North Carolina State. But the Blue Devils will be without senior forward Ryan Kelly, who re-injured his right foot in Tuesday’s victory over Clemson.

Duke announced Wednesday that Kelly is out “indefinitely.”

Now Kelly is hardly the transcendent talent that Irving — check out his NBA numbers — is. But he is critical to the Blue Devils, a 6-foot-11 matchup nightmare capable of playing outside and inside.

Indeed, after offseason surgery on his right foot, Kelly appeared fully recovered from the injury that sidelined him for the final three games last season. The Blue Devils lost two of those, to Florida State in the ACC tournament and, shockingly, to Lehigh in the NCAA tournament.

With a starting lineup that already includes guards Quinn Cook, Seth Curry and Rasheed Sulaimon, Krzyzewski most likely will turn to reserve bigs Josh Hairston, Amile Jefferson and Alex Murphy to absorb Kelly’s minutes. None of the three — Jefferson and Murphy are freshmen — averages more than 11.3 minutes, 3.1 points or 2.1 rebounds.

Tyler Thornton (21.9 minutes per game) is Duke’s most seasoned backup if Krzyzewski elects to go small, very small, with four guards and 6-10 post Mason Plumlee.

No matter, the Blue Devils, who rank third nationally in defensive efficiency, will have difficulty checking N.C. State’s C.J. Leslie and Richard Howell inside. The Wolfpack are ninth nationally in offensive efficiency and lead Division I in field goal accuracy at 53.0 percent.

So despite the old Dean Smith maxim that an injured team is most dangerous in its first game without a key player, I like State’s chances Saturday.

Even had Duke remained healthy throughout, an undefeated season was Pat Paulsen-for-President — look it up, kids — unlikely.

Yes, the Blue Devils have accomplished seniors in Plumlee, Curry and Kelly, and are Final Four-caliber. And yes, the ACC lacks depth.

But there’s a reason no one, including loaded squads such as Vegas in 1991 and Kentucky last year, has run the table in 37 years: It’s climbing-Everest-without-a-Sherpa hard.

Hard because good luck getting today’s ADD college kids to focus for every game. Hard because scholarship limits and early exits for the NBA have created parity. Hard because perfection is elusive in any sport.

To wit: As good as Alabama football has been in winning the last two national championships, it lost in both years.

“First of all, just everything has to go right,” Krzyzewski said Monday on the ACC coaches’ media call. “Health, you need veterans. Kentucky almost did it, but they had some veterans on their team last year. Yeah, I don't think you can just do it with young guys. It took a blend on that team.

“Kyrie was like an older young player, which obviously he's shown in the NBA. He's just way ahead in maturity to go along with exceptional, exceptional talent. You need good guys, where you don't beat yourself with team issues, jealousies, things like that. …

“That team had a chance because we had the big guys, depth. We had Nolan (Smith) and Kyle (Singler) as the veterans. Then we had the best player in the country in Kyrie.”

Also, pressure mounts, as UNLV learned in 1991, when as defending champion, it reached the Final Four unbeaten, only to lose to Duke.

“Overall, I think pressure has something to do with it,” Krzyzewski said. “I think one of the biggest things is you get accustomed to winning and you expect to win, but you have to keep the hunger for preparation and the hunger for competition while you're winning, while great things are happening for you. And that's very difficult.

“It's very difficult to keep your edge at that level for a long period of time. Therefore, a team has to be really good because it would have to win games when it doesn't have that edge, where talent sometimes just does that. I don't think that's our team this year. But I think you need that. …

“People start talking about you being undefeated and not talking about the game you're playing. You end up answering a lot of questions about being undefeated and not the competitor that you have to face. That can be distracting and reduce your edge in preparation.”

Such questions aren’t likely to linger long for Duke. The more pressing question is: When will Kelly return?

I can be reached at 247-4636 or by e-mail at dteel@dailypress.com. Follow me at twitter.com/DavidTeelatDP

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